1. Field of the Invention
This invention relates to a process for preparing cyclic carbonates from diols.
2. Prior Art
It is well known in the art to prepare cyclic carbonates from diols. For example, Japanese Pat. Application Kokai No. Sho 58-49377 (laid open on Mar. 23, 1983) discloses a process for preparing 1-isopropyl-2,2-dimethyl-1,3-propylene carbonate by heating 2,2,4-trimethyl-1,3-pentanediol and a dialkylcarbonate in the presence of a conventional esterifying catalyst such as para-toluenesulfonic acid to effect ester exchange reaction. The typical dialkylcarbonate used in examples is diethylcarbonate.
We carried out similar reaction in the presence of para-toluenesulfonic acid catalyst by substituting dimethylcarbonate for the diethylcarbonate. There was obtained only a small amount of cyclic carbonate. It was found that the reaction does not proceed smoothly with every dialkylcarbonate when a cyclic carbonate is prepared by reaction of a diol with a dialkylcarbonate in the presence of an acid catalyst such as para-toluenesulfonic acid.
Japanese Pat. Application Kokai No. Sho 56-133246 discloses a process of reacting a diallyl carbonate ester with a polyhydric alcohol such as diethylene glycol in the presence of a basic catalyst to form an allyl carbonate ester of a polyhydric alcohol. The carbonate obtained by this process is a chain carbonate such as ethylene glycol bisallyl carbonate. There are obtained no cyclic carbonates.